Datasheet LT3844 (Analog Devices) - 7
| Manufacturer | Analog Devices |
| Description | High Voltage, Current Mode Switching Regulator Controller with Programmable Operating Frequency |
| Pages / Page | 26 / 7 — pin FuncTions. VCC (Pin 13):. TG (Pin 15):. BOOST (Pin 16):. SW (Pin … |
| File Format / Size | PDF / 292 Kb |
| Document Language | English |
pin FuncTions. VCC (Pin 13):. TG (Pin 15):. BOOST (Pin 16):. SW (Pin 14):. Exposed Pad (Pin 17):
Model Line for this Datasheet
Text Version of Document
LT3844
pin FuncTions VCC (Pin 13):
The VCC pin is the internal bias supply so that the BOOST pin capacitor can be charged. Give decoupling node. Use a low ESR 1µF or greater ceramic careful consideration in choosing the Schottky diode to capacitor to decouple this node to PGND. Most internal IC limit the negative voltage swing on the SW pin. functions are powered from this bias supply. An external
TG (Pin 15):
The TG pin is the bootstrapped gate drive for diode connected from VCC to the BOOST pin charges the the top N-Channel MOSFET. Since very fast high currents bootstrapped capacitor during the off-time of the main are driven from this pin, connect it to the gate of the power power switch. Back driving the VCC pin from an external MOSFET with a short and wide, typically 0.02" width, PCB DC voltage source, such as the VOUT output of the regula- trace to minimize inductance. tor supply, increases overall efficiency and reduces power dissipation in the IC. In shutdown mode this pin sinks
BOOST (Pin 16):
The BOOST pin is the supply for the 20µA until the pin voltage is discharged to 0V. bootstrapped gate drive and is externally connected to a low ESR ceramic boost capacitor referenced to SW pin.
SW (Pin 14):
In step-down applications the SW pin is The recommended value of the BOOST capacitor, C connected to the cathode of an external clamping Schottky BOOST , is 50 times greater than the total input capacitance of the diode, the drain of the power MOSFET and the inductor. topside MOSFET. In most applications 0.1µF is adequate. The SW node voltage swing is from VIN during the on- The maximum voltage that this pin sees is V time of the power MOSFET, to a Schottky voltage drop IN + VCC, ground referred. below ground during the off-time of the power MOSFET. In start-up and in operating modes where there is insuf-
Exposed Pad (Pin 17):
SGND. The exposed leadframe is ficient inductor current to freewheel the Schottky diode, an internally connected to the SGND pin. Solder the exposed internal switch is turned on to pull the SW pin to ground pad to the PCB ground for electrical contact and optimal thermal performance. 3844fc For more information www.linear.com/LT3844 7 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Pin Configuration Typical Performance Characteristics Pin Functions Functional Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts
pin FuncTions VCC (Pin 13):
The VCC pin is the internal bias supply so that the BOOST pin capacitor can be charged. Give decoupling node. Use a low ESR 1µF or greater ceramic careful consideration in choosing the Schottky diode to capacitor to decouple this node to PGND. Most internal IC limit the negative voltage swing on the SW pin. functions are powered from this bias supply. An external
TG (Pin 15):
The TG pin is the bootstrapped gate drive for diode connected from VCC to the BOOST pin charges the the top N-Channel MOSFET. Since very fast high currents bootstrapped capacitor during the off-time of the main are driven from this pin, connect it to the gate of the power power switch. Back driving the VCC pin from an external MOSFET with a short and wide, typically 0.02" width, PCB DC voltage source, such as the VOUT output of the regula- trace to minimize inductance. tor supply, increases overall efficiency and reduces power dissipation in the IC. In shutdown mode this pin sinks
BOOST (Pin 16):
The BOOST pin is the supply for the 20µA until the pin voltage is discharged to 0V. bootstrapped gate drive and is externally connected to a low ESR ceramic boost capacitor referenced to SW pin.
SW (Pin 14):
In step-down applications the SW pin is The recommended value of the BOOST capacitor, C connected to the cathode of an external clamping Schottky BOOST , is 50 times greater than the total input capacitance of the diode, the drain of the power MOSFET and the inductor. topside MOSFET. In most applications 0.1µF is adequate. The SW node voltage swing is from VIN during the on- The maximum voltage that this pin sees is V time of the power MOSFET, to a Schottky voltage drop IN + VCC, ground referred. below ground during the off-time of the power MOSFET. In start-up and in operating modes where there is insuf-
Exposed Pad (Pin 17):
SGND. The exposed leadframe is ficient inductor current to freewheel the Schottky diode, an internally connected to the SGND pin. Solder the exposed internal switch is turned on to pull the SW pin to ground pad to the PCB ground for electrical contact and optimal thermal performance. 3844fc For more information www.linear.com/LT3844 7 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Pin Configuration Typical Performance Characteristics Pin Functions Functional Diagram Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts
